This invention relates generally to electrodes for use in electrodialytic processes and, more specifically, to a bipolar electrode that produces hydroxyl ions on a side facing an anode and hydrogen ions on the opposite side nearest the cathode in a multi-compartment electrolytic cell.
Techniques exist to employ water splitting membranes in electrodialytic processes. One approach, disclosed in U.S. Pat. No. 4,238,305, employs a process that uses a two compartment electrodialytic unit that alternates bipolar ion exchange membranes and cation permselective ion exchange membranes between the two electrodes. This process electrodialytically converts impure solutions of sodium bicarbonate to high purity carbon dioxide and high purity and concentrated sodium hydroxide. However, the process disclosed in this reference is not cost effective when compared to the reliable lime-soda process traditionally employed to produce sodium hydroxide. This process has relatively high resistance that prevents it from being practiced at high current densities. The bipolar ion exchange membranes would be unstable if exposed to the high temperatures needed to reduce the electrolyte's resistance in the electrolytic cell. Further, it is unlikely that high current density operation could be achieved simultaneously with the complete removal of sodium from the solution, since the conductivity of the solution is reduced when the sodium bicarbonate is depleted. Anion impurities, such as sulfate, must be added to the solution to improve the performance of the process.
Bipolar membranes previously employed in water splitting applications transport water, but are limited by their ability to operate in strongly corrosive solutions, their inability to withstand high operating temperatures and their relatively high operating resistance.
These problems are solved in the process and in the design of the water ionizing electrode of the present invention by providing a water ionizing electrode for use in an electrodialytic process capable of producing acids and alkali solutions from neutral salts.